A motive in the stabbing is unclear, but French President Emmanuel Macron said on Twitter that “France once again pays the price of blood, but does not give an inch to the enemies of freedom,” and “I salute on behalf of all the French people the courage of the policemen who neutralized the terrorist.”

Paris Prosecutor Francois Molins said on French radio that the investigation into the knife attack is in the hands of the counter-terrorism unit, and that several witnesses heard the attacker shout “Allahu akbar,” Arabic for “God is great.” But Molins did not discuss a motive.

The U.S. official briefed on the situation said witnesses stated that the suspect looked emotionally disturbed and was pacing and muttering before the incident. Paris and U.S. officials said the stabbing is being investigated as a terror attack.

Forensic officers and French police stand in Monsigny street in Paris after one person was killed and several injured by a man armed with a knife, who was shot dead by police in Paris on May 12, 2018.Geoffroy Van Der Hasselt / AFP – Getty Images

The Islamic State terror group claimed in a statement from its Amaq media arm claiming that the attacker was a “soldier” of the group, according to security consulting firm and NBC News partner Flashpoint Intelligence.

The statement contains no evidence to back up the group’s claim, and it was not clear whether the suspect was inspired by or even a follower of the terror group.

The stabbing happened at around 9 p.m. local time (3 p.m. ET), the U.S. official said.

French Prime Minister Edouard Philippe said in an interview broadcast by BFMTV that the identity of the attacker had not been established. He said that the attacker was killed nine minutes after police were called to the scene.

BFM television interviewed an unnamed witness in a restaurant who said a young woman was at the entrance when “a man arrived and attacked her with a knife.” A friend came to her aid and the attacker left, “hitting on all the doors, all the shops,” the witness told BFM. He turned onto another street, and everyone scattered, the witness said.

“I was having a drink with friends and we heard a boom,” a witness named Gloria, who had been in a nearby bar, recounted on Saturday night. She said she went outside to see what happened and “I saw a guy lying on the ground.”

France has been on edge after a series of terror attacks in the country.